Also, yes you are correct, but it really depends. The Halachot are very complicated. There is even a Gemara in Gitin about this I believe.
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Hacham GabrielJan 8 '12 at 17:41

Could you post the case, he say "ze lo neder". That may clarify his intent.
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YDKJan 8 '12 at 17:57

1

One could interpret that as saying that since she did not use a language of neder or shevua, it doesn't take hold. But when there is a mitzva, even a weaker language is sufficient. (I'm not saying he is saying that, but it's an example of an interpretation that is more plausible than "nedarim are only on mitzvos.)
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YDKJan 8 '12 at 21:45